Extraction selectivity of organic solutions of a cyclic polyether with respect to the alkali cations

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Abstract

The extraction of alkali cations (Li+, Na+, K+, Rb+, Cs+) by the neutral cyclic polyether dibenzo-18-crown-6 dissolved in various nitrobenzene-toluene mixtures has been studied. Thermodynamic data have been so obtained regarding the alkali cation-cyclic polyether reaction. The affinity of the cyclic polyether for the alkali cations has been found to vary in the order K+ > Rb+ > Cs+ > Na+ > Li+ for all the diluents compositions. Moreover the independence of the selectivity constant, defined as the equilibrium constant of the reaction: Cs+ + MSXCsSX + M+ (where M is the alkali cation, S the cyclic polyether, X the picrate ion and the bar indicates organic species) on the diluent composition seem to indicate that the complexes formed with the cyclic polyether are isosteric, i.e. with size, shape and external electronic distribution independent of the chemical nature of the cation.

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Permanent address: “Rudjer Bošković Institute”, Zagreb, Yugoslavia.

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